In manufacturing and other settings, crated and boxed items are typically grouped together in a stacked arrangement to facilitate handling, storage, loading and shipping. However, as a consequence of placing the plurality of boxed items in stacked arrangement upon one another, the boxes must be secured in order to remain in place in the stack. The securing process is oftentimes referred to as "unitizing." A common form of unitizing includes the boxed items being placed upon a pallet (i.e., the boxed items are "palletized"). As those skilled in the art will appreciate, the boxed items are generally placed in a cube or other rectangular prism arrangement, with a plurality of boxes forming each of the several sides, top, and bottom. Accordingly, a typical stack of boxes may be considered a three dimensional array of boxes of l.times.m.times.n (in describing the present invention, an [x, y, z] Cartesian coordinate system will be discussed below, wherein l and m are variables which lie in a plane above and parallel to the x-y plane and n describes the height z above the x-y plane).
It will be immediately appreciated that numerous factors contribute to the stability (both vertical and lateral) of the array of boxes. The requirement for the lateral stability is increased as the unitized stack is moved from one location to another. For example, the stacking strength of a load of boxed items depends on the pattern or layout of each tier. In many instances a column stack yields the greatest vertical strength, but has little lateral stability. Other interlocking patterns increase lateral strength, at the expense of vertical strength, and may also improve the space utilization of the pallet. The balancing of these several factors (i.e., vertical strength, lateral stability, and space utilization) tends to produce a wide variety of pallet patterns depending on the type and size of the boxed items being unitized.
Since lateral stability is oftentimes sacrificed for optimization of space utilization and/or vertical stability, virtually every array requires some sort of restraining device. Previously, several methods have been utilized to unitize palletized arrays.
One example of a prior method comprised placing a net type device over the entire stack of boxed items, with the net then being gathered together about the base of the stack. This method, however, had several drawbacks. First, placing the net over the stack of boxed items required either being above the elevation of the stack or "casting" the net over the stack. Second, in addition to being bulky and cumbersome, a large supply of nets needed to be stocked in order to unitize the items in advance prior to shipping (or to merely move the palletized items within the confines of a warehouse).
Other methods which have been tried to improve lateral stability of stacks were the provision of a horizontal "strap" of material about the stack, use of an adhesive on the surfaces of the boxes which come into contact with one another, and shrink wrapping the palletized load. However, each of these methods suffers from drawbacks. First, strapping typically must be secured about the stack so tightly that damage to the boxes contacted by the strapping may result. Second, adhesives must provide a high shear strength to resist lateral forces, but low tensile strength in order to be disassembled without damaging the box. Third, the heat required for shrinkwrapping tended to require additional costs over other available methods.
The drawbacks associated with these methods lead to a method of unitizing by wrapping a stretch material about the array. Typical examples of this method of unitizing are illustrated by U.S. Pat. Nos. 4,549,388, 4,369,614, 4,429,514 and 4,095,395. In general these patents disclose devices which wind a plastic film about the stack of boxed items by securing the first end of the film to the pallet and then either rotating the pallet (relative to the supply of film) or moving the supply of film about the stack. The film is typically wound so as to form a completely overlapping "cocoon" of film about the stack. Thus, the entire outermost sides/edges of the stack of boxed items become encircled in the process of wrapping the plastic film. This method, however, suffers several drawbacks. First, a great amount of plastic film material is used which is not actually required to hold the items in place. This drawback is not only wasteful of the plastic material, but also adds unnecessary shipping costs. A second drawback is that the material must somehow be fastened at its first end which is inconvenient and time consuming. Finally, when the plastic is removed, it is not reusable so it must be either recycled or taken to a landfill. As previously noted, this last drawback is exacerbated since more plastic film is used than is required.
Additional U.S. patents disclose forming the sheet of plastic film material into a "rope" which is then wrapped about a portion of the array of items. In general, the roping devices merely gather the plastic film together from the film's side edges (about its longitudinal length) into an elongate continuous band. This process forms a high strength wrap which is typically used at the ends of the film wrapping process or to wrap about the items in various configurations. Examples of such devices are found in U.S. Pat. Nos. 4,845,920; 4,807,427; 4,204,377; 4,255,918; 4,432,185; and 4,235,062. However, each of the foregoing patents does not solve the problem of using a large amount of unneeded plastic film material and does not provide for a selectively releasable adhesive to secure the first or last end of the film during the wrapping procedure.
Therefore, there arises a need for a unitizer method and system which uses a stretch detackification adhesive tape to wrap predetermined portions of the stack of boxed items to provide lateral stability. Such a method should preferably use less material than other previous methods, and should easily secure the tape at strategic portions of the array--while being detackified at other locations so as to be releasable (i.e., the detackified tape should preferably be releasable such that it does not damage the surface to which it is applied).